Android NDK: calling java method from JNI C class

Question

I have JNI method where I am trying to call Java method. Here is my JNI code

void DummySink::afterGettingFrame(unsigned frameSize, unsigned numTruncatedBytes,
                  struct timeval presentationTime, unsigned /*durationInMicroseconds*/) {

     __android_log_print(ANDROID_LOG_VERBOSE, "RTSP", "Frame: %c", propRec->sPropBytes);
     jmethodID mid;
     jclass handlerClass = env9->FindClass("ob/android/Stream");
     if (handlerClass == NULL) {
         __android_log_print(ANDROID_LOG_VERBOSE, "RTSP-Error", "Class");
     }
     mid = env9->GetMethodID(handlerClass, "onResponse", "([B)V");
     if (mid == NULL) {
         __android_log_print(ANDROID_LOG_VERBOSE, "RTSP-Error", "Method");
     }

     jbyteArray jbArray = env9->NewByteArray((int)propRec->sPropLength);
     env9->SetByteArrayRegion(jbArray, 0, (int)propRec->sPropLength, (jbyte*)propRec->sPropBytes);

     //jobject theClass = env9->FindClass("ob/android/Stream");

     env9->CallVoidMethod(handlerClass, mid, jbArray);

}

Here is the Java code that I have

public void onResponse(byte[] str) 
    { 
        Log.v("Response", "Java");
    }

I am receiving following crash

03-08 16:01:05.915: W/dalvikvm(17552): JNI WARNING: can't call Lob/android/Stream;.onResponse on instance of Ljava/lang/Class;
03-08 16:01:05.915: W/dalvikvm(17552):              in Lob/android/Stream;.stream:()V (CallVoidMethodV)

After applying Mah's answer, here is the exception I am receiving

03-08 16:40:20.646: W/dalvikvm(4076): JNI WARNING: JNI method called with exception pending
03-08 16:40:20.646: W/dalvikvm(4076):              in Lob/android/Stream;.stream:()V (NewByteArray)
03-08 16:40:20.646: W/dalvikvm(4076): Pending exception is:
03-08 16:40:20.646: I/dalvikvm(4076): java.lang.NoSuchMethodError: no method with name='onResponse' signature='([B)V' in class Lob/android/Stream;
03-08 16:40:20.646: I/dalvikvm(4076):   at ob.android.Stream.stream(Native Method)
03-08 16:40:20.646: I/dalvikvm(4076):   at ob.android.Stream.<init>(Stream.java:28)
03-08 16:40:20.654: I/dalvikvm(4076):   at ob.android.MainActivity.startRecording(MainActivity.java:203)

Now onResponse method is static.

You must check for and handle exceptions after any JNI call that can throw an exception. CallVoidMethod being a prime example. See developer.android.com/training/articles/… — fadden
– fadden, Commented Mar 9, 2013 at 0:56

mah · Accepted Answer · 2013-03-08 11:11:56Z

11

Your Java method is an instance method (not static), but your native code isn't referring to any specific instance of ob.android.Stream to call onResponse() for.

When calling CallVoidMethod(), the first parameter is to be the instance (object) you're running the method against, not the class itself. The class itself would be used if you were using CallStaticVoidMethod().

answered Mar 8, 2013 at 11:11

mah

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4 Comments

Jackie Over a year ago

Any chance of getting a little more detail when I change to.. jmethodID method = env->GetMethodID(obj, "playA", "()V"); I see... error: invalid conversion from 'jobject {aka _jobject*}' to 'jclass {aka _jclass*}' [-fpermissive]

mah Over a year ago

@Jackie GetMethodId() wants the class to get the method id from, not an object as you appear to be using. If you don't already have the class for that object available, you can get it from that obj by using GetObjectClass()

Evan Leis Over a year ago

Correction: The first argument to CallVoidMethod must be the java environment to run the method in.

mah Over a year ago

@EvanLeis if the calling environment were C you would be correct. Since it's C++ though, the java environment is not the first parameter because it's the object the message is being called against, as in env->CallVoidMethod(). You can tell that C++ is the language at play here from the code in the question.

Georgi Atsev · Accepted Answer · 2017-09-07 15:41:24Z

0

I would like to add one more solution to the NoSuchMethodError problem, that although might not be the case here, might save some of you a lot of hours of debugging.

For me, there was a proguard config file that I had to edit. Otherwise all non-static java methods that aren't called in the java code, get optimized out and the native C++ code isn't able to find them.

edited Sep 7, 2017 at 15:41

answered Aug 28, 2017 at 13:33

Georgi Atsev

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